Electrolytic manganese



United States Patent I ELECTROLYTIC MANGANESE James H. Jacobs, Marietta,Ohio, and Michael C. Carosella, Niagara Falls, and James B. Culbertson,Lockport, N. Y., assignors to Union Carbide Corporation, a corporationof New York No Drawing. Application April 2, 1956,

Serial No. 575,313

2 Claims. ((31. 204-105 The present invention relates to an improvedelectrolytic maganese process and, more particularly, to a processemploying electrolyte modifiers that control the formation of thedeposited manganese metal.

In the production of metallic electrolytic manganese, the form of thedeposited metal is of the greatest importance since it influences theefliciency of the process, the purity of the deposited metal, and theease with which the deposited metal can be stripped from the cathode.

If the deposited metal is coarsely granular,it may build up onthe'cathode in small nodules that grow radially,

forming a cauliflower-like structure from which electrolyte is noteasily washed. Also, in this form the metal is not easily stripped fromthe cathode material (if this is not the same metal as that beingdeposited), since the metal tends to come off in individual nodulesrather than in sheets or plates. In some processes, the deposited metalis removed from the cathodes by flexing or vibrating the latter; if thedeposit is nodular, it tends to flex with the cathode and does not breakloose. Another difficulty encountered is treeing; that is, some nodulesmay grow at a much greater rate than the average, thus becoming muchextended above the surface of the cathode deposit. In some cells thismay make it mechanically diflicult to remove the cathodes, or may upsetcurrent distribution (thus aggravating the condition). In addition, thenodules tend to be broken off and lost during handling, decreasing metalrecovery.

A further difiiculty encountered is the influence of cathode metalstructure on deposition time. Obviously, if cathodes must be changedfrequently, the overall process etficiency is greatly reduced. Asmentioned above, treeing of the cathode metal, once started,becomes'selflpropagating and the extension or growth of the trees can be2,805,195 Patented Sept. 3, 1957 'ice M It is an object-of the presentinvention to extend by reducing the frequency at which cathodes must beremoved, stripped, prepared and reinserted in cell.

Another object of .the invention is to produce electrolytic manganesemetal of improved purity.

A further object ofthe invention is to produce metallic manganese metalthat is sound, dense, less friable and of greater thickness thanotherwise obtained, and, therefore, easier to handle and use.

The electrowinning of some metals is much more easily accomplished thanothers; copper, silver, and nickel may be electrodeposited withoutparticular difliculty. One of the metals which is more difficult toobtain electrolytically is manganese which tends to deposit in irregularfashion and in nodular form, and is very prone to form trees.

Prior practice for electrowinning of manganese was such' that not morethan a 25- to 30-hour deposition period could be achieved. If it wasattempted to continue deposition beyond this length of time, the qualityof the metal degenerated and became unacceptable.

By the process of this invention, high-quality manganese metal can beelectrodeposited for periods of two to four times as long as is possiblewith prior processes.

The present invention comprises a process for electrowinning ofmanganese from an electrolyte composed sub- I stantially of manganesesulphate, ammonium sulphate, and potassium sulphate which serves as asmoothing agent. The presence of specific quantities of potassiumsulphate in the electrolyte has a marked effect upon the character ofthe manganese metal deposited at the cathode.

By the addition or other provision of potassium sulphate in theelectrolyte, the character of deposited metal is altered from soft todense, hard compact metal. This makes it possible to increase thecontinuous plating time by a factor of from two to four. Inclusion ofpotassium sulphate in the electrolyte has'made it possible in some casesto obtain continuous deposition of dense, hard manganese metal forperiods up to 72 and 96 hours, a

far longer period than is possible in the absence of this additionagent, and appreciably longer than has been pos-. sible with anyadditive of the prior art.

As is well known in the art, a small amount of sulphur dioxide is addedto the cell feedsolution (in a concentration of about 0.1 to 1.0 gramper liter) to stabilize the solu tion and to increase the currentefiiciency. I

More specifically, it has been found that the provision of between 20and grams per liter of potassium sulphate in the electrolyte will beeffective in extending the deposition time without any sacrifice incurrent efficiency.

The data in the table below show that the progressive I increase from3.3 to 25 gms. per liter in the concentration of potassium sulphate inthe cell feed over a 16-month period enabled the operators to extend theplating time by 50% with no drop in the current efficiency. This meansthat the plate is 50% thicker and that the appearance was good at theend of 72 hours.

the deposition time, and thus simplify and improve the elficiency of theprocess for the electrowinning of manganese Table Grams per Liter inCell Feed Current Plating Run Time, Appearance N0. eieney Hrs.

M11 K K3504 (NHQgSO;

1. 48 3. 3 115 61 48 Generally good but nodular. 1.72 3.8 118 61 48 and.2. 32 5. 2 114 62 72 Surface not good. 3. 60 8. 120 63 48 Good. 6.2013.8 132 62 48 Nodular, me-

dium base. 6. 5 14. 6 137 61 48 Generally good.

but nodular. 8.0 17.8 136 62 48 Good. 8.50 19.0 r 133 65 48 Very good.9.75 21.8 133 62 72 Medlumtothiok I basewith L a F l nodules.

10.7 23.8 128 64 "7'2 Good. 10.8 7 2m ,125 v 63.6 72' Good. ms 25.=--'123- 63 I 72 Good. 11-.0: 2cc 4 can i '72 Good.

lhiotnieasured.

mammalian tearsaehssiayer 'oiaieaianrancaassaarraum the cathode. The

product had built up on this base in-the form oi' nodules.

The ohjectivei of thei tests which yieldedthe ahoye data was toproduce'thickplate' of dense structure and surface. Fo'r'thes'atuecurrente'fiiciencythe thickn ss-of'rthe" plate is'adirect functionof the time;

Therefore; the latingiime was extended asidn as was compatible with theproduction of'dense' plate having a oftrees or' nodular struct 'ue.'lhedata show that 48 1mm plate was not uniformly oouf until the 150-tassii'irnsulphate c'oncentration approached 2Q; gms. p'er liter'of cellfeed; also'that the attempt town 72 hour'sin run No: 3 was notsuccessful-because the surface appeararice' was not good enough; Fromrun No; 9" on, the-plate was" dense and thick with 72-hour plating timeand was esse'n'tially free of trees or nodular structure since thepotassium sulphate'concentr'ation was increased -frorn= 2f to about 25'gnfis. per liter.

The upper limit of 70 gms. potassium sulphate per liter was chosen asbeing the limit of solubility in a synthetic cell feed produced frommaterials essentially free ofsodium but containing ammonium sulphate andmanganese sulphate in normal amounts. This limit is the concentration ofpotassium sulphate compatible with the other constitutentsof the normalcell feed for the electrowinning of manganese, i. e., manganese andammonium sulphates with sodium sulphate as an impurityand sulphurdioxide addition as known to the prior art. Experiments on the use ofvarious concentrations of sodium sulphate in the absence of'potassiumhave shown that salt is neither harmful nor beneficial. Consequently, itis considered as an impurity but it has a marked efi ect on thesolubility of potassium sulphate. It has not been determined as to whenthis concentration of sodium sulphate becomes critical. V 7

However, early experiments showed that sodium sulphate 38 gms. per literpermitted a concentration of 3 0 gms; per liter of potassium sulphate(68 gms./l. total) in the standard cell feed. This was the maximumobtainable with this sodium concentration. Consequently, a figure of70grr1s. potassium sulphate per liter'was specified as a practicaltop'liinit. This assumes that the concentration of potassium sulphatecould easily reachthis figure in the standard cell feed with a minimumof sodium sulphate present since potassium salts are generally speakingmore soluble thanj sodium-salts.

In an exam le ofthe process of the invention, an'elec- V trolyte wascontinually electrolyzed to produce a catholyte containing. about 11.0grams per liter manganese, 128.5 grams per liter ammonium sulphate, 0.75gram per liter sulphur dioxide, and 32 grams per liter potassiumsulphate in the cathode compartment of a: diaphragm electrolytic cellemploying 99% lead-1% silver alloy anodes and stainless steel cathodes.The cathode current density employed was abgurfl 40' amperes per squarefoot and a catholytepH of about 815 was maintained; Solid, densemanganese" metal was deposited on the cathode for 48 hours beforea'fi'n'e nodular structure began to appear; There was" noevidence of'oeeinor loss in current e'fiictencyat any time during the'de'posiiionperiod;

' This isacontinuatien in part of our depending applica tion- Serial No.378,403" filed September 3, 1953', now abandoned; v v

Vth'atis claimed is": I a

1. In a process for the electrowinning ofmetallic manganeseemploying adiaphragm compartment. cell and an electrolyte comprising an' aqueousmanganese and ammoniufm sulphate solution containing an amount ofsulphur'dioxide' efiective to stabilize the solution and increase thecurrent eificie'ucy, the improvement which comprises providing andmaintaining in said electrolyte solution during electrolysisb'etween'about 20 and grams per liter of potassium sulphate, whereby athick, dense metallic manganese deposit substantially free of nodules isproduced'.

' 2; A'p'ro'ces's for the electrowinning' of metallic manganeseemploying a diaphragm compartment cell and an electrolyte comprising anaqueous manganese and ammoniun-i sulphate solution containing an amountof sulphur dioxide effective" tostabilize the solution and increase thecurrent efficiency comprising, providing in said cell an aqueoussolution containing manganese sulphate, ammonium sulphate, sulphurdioxide, and between 20 and 70 grams per liter of potassium sulphate,and electrolyzing said solution to-for'm at the cathode of said cell, athick, dense metallic manganese deposit substantially free of nodules.

7 Ref rences crted in'tue file of thispaterit I V 'UNITEDSTALTES PATENTS'2',4'46 ',3l3" Vedensky L Aug. 3, 1948

1. IN A PROCESS FOR THE ELECTROWINNING OF METALLIC MANGANESE EMPLOYING ADIAPHRAGM COMPARTMENT CELL AND AN ELECTROLYTE COMPRISING AN AQUEOUSMANGANESE AND AMMONIUM SULPHATE SOLUTION CONTAINING AN AMOUNT OF SULPHURDIOXIDE EFFECTIVE TO STABILIZE THE SOLUTION AND INCREASE THE CURRENTEFFICIENCY, THE IMPROVEMENT WHICH COMPRISES PROVIDING AND MAINTAINING INSAID ELECTROLYTE SOLUTION DURING ELECTROLYSIS BETWEEN ABOUT 20 AND 70GRAMS PER LITER OF POTASSIUM SULPHATE, WHEREBY A THICK, DENSE METALLICMANGANESE DEPOSIT SUBSTANTIALLY FREE OF NODULES IS PRODUCED.